Various commercial products exist to help vehicle owners maintain the appearance and cleanliness of vehicle surfaces. Typical of such products are waxes, pastes, and sealants that claim to help protect the surface from environmental damage while providing a high gloss, slick appearance. Typically, such products provide hydrophobic surfaces (e.g., as in the case of carnauba wax, silicone waxes, and sealants) which often yield a water contact angle of about 90°. This effect is known as ‘water beading’.
Upon drying, water beading leaves behind dirt residue in the form of spots caused by concentration of dirt or other contaminants present in the water. This problem gets worse when the water is especially dirty, for example, as found in slush, mud, or road spray.
The effect of surface roughness and porosity on wetting has been studied (see, for example, A. B. D. Cassie and S. Baxter, “Wettability of Porous Surfaces”, Trans. Faraday Soc., 1944, Vol. 40, pages 546-551). More recently, precision surface structuring has been studied in an effort to develop self cleaning “lotus effect” type surfaces; see, for example, K. J. Kubiak et al., “Wettability versus roughness of engineering surfaces”, Wear, 2011, Vol. 271, pp. 523-528. However, large-scale production of such surfaces is not necessarily simple given that many of them are made via a process such as lithography, etching, or thin-film deposition that may not easily be transferred to complex curves found on vehicles.
Recent years have seen the introduction of various commercial products claiming to provide for ‘water-sheeting’ rather than ‘water beading’ behavior, which may reduce or eliminate water spots on drying. Water-sheeting results from the hydrophilic surface which can be effectively wet by water, thereby allowing water to drain from the surface. However, current products that provide long-lasting, durable water-sheeting surfaces typically have drawbacks such as unacceptably high levels of solvent needed to deposit them, or require cumbersome thermal curing or radiation curing.
Accordingly, there is a need for hydrophilic surface coatings and uncomplicated methods of making them that provide a durable, water-sheeting effect without requiring the use of high levels of solvent or cumbersome curing conditions in their preparation. Moreover, it is desirable that such surfaces are aesthetically acceptable in appearance.